1. Field of the Invention
The present invention relates generally to an CDMA mobile communication system, and in particular, to an apparatus and method for transmitting TFCI (Transport Format Combination Indicator) bits used during data transmission over a downlink shared channel in an CDMA mobile communication system.
2. Description of the Related Art
In a mobile communication system, a plurality of users located in the same cell share a downlink shared channel (DSCH) on a time-division basis. The DSCH is established in association with a dedicated channel (DCH) of every user. The DCH includes a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH). In particular, the DPCCH is also used as a physical control channel for the DSCH. Therefore, the DPCCH transmits control signals of the associated DCH and DSCH. The control signals include a TFCI (Transport Format Combination Indicator) that is transmitted by encoding 10-bit information into 30 bits. That is, information on an amount of data is expressed by 10 bits, and the 10-bit information is encoded into 30 bits for transmission over a physical channel. Therefore, the DPCCH should simultaneously transmit TFCI for the DCH and TFCI for the DSCH. Herein, TFCI for the DCH will be referred to as TFCI field#1 or first TFCI, and TFCI for the DSCH will be referred to as TFCI field#2 or second TFCI.
A method for simultaneously transmitting the TFCI field#1 and the TFCI field#2 over the DPCCH is divided into two methods: a hard split method and a logical split method.
In the logical split method, one TFCI comprised of the TFCI field#1 and the TFCI field#2 in a specific ratio is encoded into 30 coded symbols with a (30,10) punctured Reed-Muller code (or sub-code second order Reed-Muller code). A ratio of the TFCI field#1 to the TFCI field#2 is one of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 and 9:1.
In the hard split method, a 5-bit TFCI field#1 and a 5-bit TFCI field#2 are encoded with a (15,5) punctured bi-orthogonal code, and then multiplexed into 30 coded symbols.
FIG. 1 illustrates a structure of a transmitter based on the hard split method. Referring to FIG. 1, a (15,5) bi-orthogonal encoder 100 encodes a 5-bit TFCI field#1 for the DCH into 15 coded symbols with a (15,5) punctured bi-orthogonal code, and provides the 15 coded symbols to a multiplexer 110. At the same time, a (15,5) bi-orthogonal encoder 105 encodes a 5-bit TFCI field#2 for the DSCH into 15 coded symbols with the (15,5) punctured bi-orthogonal code, and also provides the 15 coded symbols to the multiplexer 110. The multiplexer 110 then time-multiplexes the 15 coded symbols from the encoder 100 and the 15 coded symbols from the encoder 105, and outputs 30 symbols after arrangement. A multiplexer 120 time-multiplexes the 30 symbols output from the multiplexer 110 and other signals (for example: Transmission Power Control bits (TPC), Pilot bits, and data bits), and provides its output to a spreader 130. The spreader 130 spreads the output signal of the multiplexer 120 with a spreading code provided from a spreading code generator 135. A scrambler 140 scrambles the spread signal with a scrambling code provided from a scrambling code generator 145.
FIG. 2 illustrates a procedure for exchanging signaling messages and data between a Node B and RNCs (Radio Network Controllers) for the hard split method defined in the existing 3 GPP (3rd Generation Partnership Project). Referring to FIG. 2, if transmission data of the DSCH is generated, a radio link controller (RLC) 11 of an SRNC (Serving RNC) 10 transmits the DSCH data to a MAC-D (Medium Access Control-Dedicated channel) 13 of the SRNC 10 in step 101. A primitive transmitted at this moment is MAC-D-Data-REQ. In step 102, the MAC-D 13 of the SRNC 10 transmits DSCH data received from the RLC 11 to a MAC-CSH (MAC-Common/Shared channel) 21 of a CRNC (Control RNC) 20. A primitive transmitted at this moment is MAC-CSH-Data-REQ. In step 103, the MAC-C 21 of the CRNC 20 determines (schedules) a transmission time for the DSCH data received in the step 102 from the MAC-D 13 of the SRNC 10, and then, transmits the DSCH data along with its associated TFI (Transport Format Indicator) to an L1 (Layer 1) 30 of a Node B (hereinafter, the term “Node B” refers to a base station). A primitive transmitted at this moment is MPHY-Data-REQ. In step 104, the MAC-D 13 of the SRNC 10 transmits transmission data of the DCH and its associated TFI to the L1 30 of the Node B. A primitive transmitted at this moment is MPHY-Data-REQ. The data transmitted in the step 103 is independent of the data transmitted in the step 104, and the L1 30 of the Node B generates a TFCI that is divided into a TFCI for the DCH and a TFCI for the DSCH. In the steps 103 and 104, the data and the TFIs are transmitted using a data frame protocol.
After receiving the data and the TFIs in the steps 103 and 104, the L1 30 of the Node B transmits the DSCH data over a physical DSCH (PDSCH) to an L1 41 of a UE (User Equipment; hereinafter, the term “UE” refers to a mobile station) 40 in step 105. In step 106, the L1 30 of the Node B transmits the TFCI to the L1 41 of the UE 40 using the DPCH. The L1 30 of the Node B transmits the TFCIs created with the TFIs received in the steps 103 and 104, using the fields for the DCH and the DSCH.
FIG. 3 illustrates a procedure for exchanging signaling messages and data between a Node B and an RNC for the logical split method. Referring to FIG. 3, if DSCH data to be transmitted is generated, an RLC 301 of an RNC 300 transmits the DSCH data to a MAC-D 303 of the RNC 300 in step 201. A primitive transmitted at this moment is MAC-D-Data-REQ. Upon receipt of the DSCH data from the RLC 301, the MAC-D 303 transmits the DSCH data to a MAC-C/SH (MAC-Common/Shared channel) 305 in step 202. A primitive transmitted at this moment is MAC-C/SH-Data-REQ. Upon receipt of the DSCH data, the MAC-C/SH 305 determines a transmission time of the DSCH data and then transmits a TFCI associated with the DSCH data to MAC-D 303 in step 203. After transmitting the TFCI to the MAC-D 303 in the step 203, the MAC-C/SH 305 transmits the DSCH data to an L1 307 of the Node B in step 204. The DSCH data is transmitted at the time determined (scheduled) in the step 203. Upon receipt of the TFCI for the DSCH data transmitted from the MAC-C/SH 305 in the step 203, the MAC-D 303 determines a TFCI for the DSCH and transmits the TFCI to the L1 307 of the Node B in step 205. A primitive transmitted at this moment is MPHY-Data-REQ.
After transmitting the TFCI for the DSCH, the MAC-D 303 determines a TFCI for the DCH and transmits the DCH data along with the TFCI for the DCH to the L1 307 of the Node B in step 206. A primitive transmitted at this moment is MPHY-Data-REQ. The DSCH data transmitted in the step 204 and the TFCI transmitted in the step 205 are related to the time determined in the step 203. That is, the TFCI in the step 205 is transmitted to a UE 310 over the DPCCH at a frame immediately before the DSCH data in the step 204 is transmitted over the PDSCH. In the steps 204, 205 and 206, the data and the TFCIs are transmitted using a frame protocol. Particularly, in the step 206, the TFCI is transmitted through a control frame. In step 207, the L1 307 of the Node B transmits the DSCH data over the PDSCH to an L1 311 of the UE 310. In step 208, the L1 307 of the Node B creates a TFCI using the respective TFCIs or TFIs received in the steps 205 and 206, and transmits the created TFCI to the L1 311 using the DPCCH.
Summarizing the logical split method, the MAC-C/SH 305 transmits DSCH scheduling information and TFCI information of the DSCH to the MAC-D 303 in the step 203. This is because in order to encode the TFCI for the DSCH and the TFCI for the DCH in the same coding method, the MAC-D 303 must simultaneously transmit the DSCH scheduling information and the TFCI information to the L1 307 of the Node B. Therefore, when the MAC-D 303 has data to transmit, a delay occurs until the MAC-D 303 receives the scheduling information and the TFCI information from the MAC-C/SH 305 after transmitting the data to the MAC-C/SH 305. In addition, when the MAC-C/SH 305 is separated from the MAC-D 303 on the lur, i.e., when the MAC-C/SH 305 exists in the DRNC (Drift RNC) and the MAC-D 303 exists in the SRNC, the scheduling information and the TFCI information are exchanged on the lur, causing an increase in the delay.
Compared with the logical split method, the hard split method can reduce the delay because information transmission to the MAC-D is not required after scheduling in the MAC-C/SH. This is possible because the Node B can independently encode the TFCI for the DCH and the TFCI for the DSCH in the hard split method. In addition, when the MAC-C/SH is separated from the MAC-D on the lur, i.e., when the MAC-C/SH exists in the DRNC and the MAC-D exists in the SRNC, the scheduling information is not exchanged on the lur, preventing an increase in the delay. However, according to the foregoing description, the information amounts (bits) of the TFCIs for the DCH and the DSCH are fixedly divided in a ratio of 5 bits to 5 bits, so that it is possible to express a maximum of 32 information for the DCH and the DSCH, respectively. Therefore, if there are more than 32 sorts of information for the DSCH or DCH, the hard split method cannot be used.